Zinc Oxide. Zinc (physical) sunblocks come in many formats with many different concentrations of zinc. I do recommend the physical blocks (zinc and titanium) because they have a very good safety profile and work very effectively.
Metals are necessary. You must remember to use both a uvb and uva sunscreen. Simply, uvb causes skin cancer and uva are more "aging rays" to protect from uvb look for octinoxate. For uva, you need a metal (zinc or titanium oxide). These metals "reflect" the suns rays away from you. You want at least 9 or 18% of these metals in your sunscreen to give you full protection. Btw there is no spf system for uva.